Molecular sieves of the crystalline aluminosilicate zeolite type are well known in the art and now comprise over 150 species of both naturally occurring and synthetic compositions. In general, the crystalline zeolites are formed from corner-sharing AlO.sub.2 and SiO.sub.2 tetrahedra and are characterized by having pore openings of uniform dimensions, having a significant ion-exchange capacity and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent crystal structure.
Other crystalline microporous compositions are known which are not zeolitic but which exhibit the ion-exchange and/or adsorption characteristics of the zeolites. These include: 1) a pure silica polymorph, silicalite, having a neutral framework containing neither cations nor cation sites as disclosed in U.S. Pat. No. 4,061,724; 2) crystalline aluminophosphate compositions disclosed in U.S. Pat. No. 4,310,440; 3) silicon substituted aluminophosphates as disclosed in U.S. Pat. No. 4,440,871; 4) titanium substituted aluminophosphates as disclosed in U.S. Pat. No. 4,500,651; 5) metal substituted aluminumphosphorus-silicon-oxide molecular sieves as disclosed in U.S. Pat. No. 4,793,984; and 6) metal substituted aluminophosphates as disclosed in U.S. Pat. No. 4,567,029. Finally, U.S. Pat. No. 4,880,761 discloses crystalline metal sulfide and metal selenide microporous materials.
The materials described above are based on either the oxide or the sulfide of the metal. For several reasons, it would be desirable to synthesize crystalline microporous materials containing framework units of MO.sub.2, MOS and MS.sub.2. The combination of sulfur and oxygen in the same molecular sieve should lead to materials with novel catalytic and adsorption properties. The reason for this is that the more acidic nature of the --SH moiety versus the --OH moiety modifies the acid activity of the metal oxysulfide and affects the distribution of acid sites within the microporous material. The modified surface selectivity of an oxysulfide microporous material would affect product distribution of hydrocarbon conversion reactions.
Klemperer and Schwartz, "Synthesis and Characterization of the Polyoxothioanions TaW.sub.5 O.sub.18 S.sup.3- and NbW.sub.5 O.sub.18 S.sup.3- ", Inorganic Chemistry, 24, 4459-61 (1985), disclose that some of the oxygen atoms in polyoxoanions can be replaced by sulfur atoms without metal center reduction and/or metal-oxygen framework degradation by treating polyoxoanions such as Nb.sub.2 W.sub.4 O.sub.19.sup.4- with hexamethyldisilthiane. However, there is no hint in Klemperer and Schwartz that some of the oxygens in molecular sieves could be replaced by sulfur. Indeed, Klemperer and Schwartz indicate that their niobium and tantalum oxothio compounds were the first such compounds to be isolated.
In contrast to the polyoxothioanions of Klemperer and Schwartz, applicants have prepared molecular sieves in which some of the oxygen atoms in the framework have been replaced with sulfur, thereby forming an oxysulfide composition. For example, applicants have taken a CoAPO-5 molecular sieve (calcined form), reacted it with hexamethyldisilthiane (HMDT) and obtained a product which had the same crystallinity as the starting material and in which about 5% of the cobalt atoms were sulfided. This material has shown activity for cracking hydrocarbons and for adsorbing various molecular species.
Applicants have prepared a wide variety of compositions which are represented by the empirical formula: EQU (M.sub.s Al.sub.t P.sub.u Si.sub.v)S.sub.w O.sub.2-w
where M is at least one metal selected from the group consisting of metals which: 1) can be incorporated into the framework structure of a microporous molecular sieve and 2) form hydrolytically stable sulfides; s is the mole fraction of M and varies from greater than zero to about 1, t is the mole fraction of Al and varies from 0 to less than 0.5, u is the mole fraction of P and varies from 0 to about 0.5, v is the mole fraction of Si and varies from 0 to less than 0.5, w is the mole fraction of S and varies from greater than zero to about 2s. Additionally, t, u and v are chosen such that when t is greater than zero u is greater than zero and s+t+u+v=1.